This invention relates generally to interlocked multiple-member composite structures and more particularly to the field of art of various shaped articles of bar shape each formed by mechanically joining at least an outer member and an inner member into a unitized structure. Examples of such structures are: screw seats or washers and seal rings of parts of mechanical apparatuses and devices; tubular structures such as steel pipe piles for architectural foundations; and column-form structural materials having cross-sections of shapes such as a circle, angle, and H-section.
More specifically, the invention concerns composite bar structures of interlocked multiple members, each bar structure comprising, for example, an aluminum alloy tubular outer member and a column-shaped inner member or core of a metal such as steel, the outer and inner members being joined mechanically at their mating interface in an interlocking manner to produce an integral bar structure. A method of producing the bar structures comprises forcibly stratifying the tubular outer member relative to the inner member which has been provided on its surface in its longitudinal and circumferential directions with a large number of projections formed integrally thereon by a process such as rolling, whereby the projections on the inner member engage interlockingly with corresponding recesses thus formed in the inner wall surface of the outer member to form a unitary bar structure.
The outer and inner members can be thus joined by a plastic deformation method such as passing the tubular outer member, with the inner member positioned therein in a telescope state, through a die by drawing or extruding, thereby to cause a shrinkage of its diameter or causing the inner member to undergo an expansion of its diameter.
As is known, spring means for functions such as absorption of vibrations and oscillations are widely used in various machines and apparatuses. For retaining these spring means, spring seats or retainers are used Also, screw or bolt seats such as washers are used for preventing loosening of the screws or bolts. Similarly, seal rings and the like are widely used. In the field of civil engineering and architecture, foundation piles are required for constructing buildings and like structures on weak ground In order to ensure ample strength and durability of such pilings, particularly with respect to corrosion resistance over a long period of time, so-called steel pipe piles and the like are used.
These items of hardware and construction materials are frequently liable to become defective by deformation due to impact, vibration, or thermal behavior with the passage of time. In order to avoid variations with time of the functional capacities of these materials, there is an increasing trend toward the use of multiple-member composite bar structures fabricated by joining unitarily outer and inner members of different materials respectively suitable for their characteristics such as mechanical strength and corrosion resistance. These outer and inner members have heretofore been joined by methods such as explosion pressure bonding and shrinkage fitting.
However, by these known methods of joining, the joining between the outer and inner members at their interface is a metallurgical bonding or a smooth pressure joining. As a consequence, in the case of repeated thermal action over a long time or the application of a great load, slippage may occur between the outer and inner members in the longitudinal or circumferential directions, whereby the structure can no longer perform as originally designed Furthermore, a large number of process steps are required in the production of these known structures, and the control and management of these steps are considerably complicated. As a result, the production cost of these known structures becomes high.